Heating system for bake ovens



May 10, 1932. E. o. ENGELS I I 1,857,447

HEATING SYSTEM FOR BAKE OVENS Original Filed sept. 11, 1950 V/V/V x I I JNVENTOJ? ZUGZ' z OSCHEZ/VGZLS ATTOJPNE? Patented May 10, 1932 UNITED STATES- PATENT OFFICE.

EUGENE OSCAR EN GELS, OI SAGINAW, MICHIGAN, ASSIGNOR TO BAKER PERKINS COIL PANY, INC., 01 SAGINAW, MICHIGAN, A. CORPORATION OF NEW YORK HEATING SYSTEM FOR BAKE OVENS Application filed September 11, 1930, Serial No. 481,112. Renewed August 20, 1981.

This invention relates to bake ovens heated by circulating hot gases from a furnace through radiating flues in the baking chamber and back through the furnace, venting ofi' enough of the gases of combustion to balance the intakeof air necessary for combustion.

The object of my invention is to provide a bake-oven heating system of this type wherein a sub-atmospheric pressure of the hot gases 'is established and maintained Within the radiating fiues or flue radiator, and the furnace. Keeping the pressure of the gases circulating within such a closed circuit slightly 5j below that of the atmosphere presents the following advantages:

First, if leaks develop in the radiating flues, the leakage will be from the baking chamber into the flues, instead of from the fiues outgo ward into the baking chamber. Thus smoke and soot are kept out of the baking atmosphere and prevented from coming into contact with the goods being baked.

Second, it makes easier the lighting of the 88 pilot and main burner if gas or oil is used as fuel, since it eliminates back pressure in the furnace at the fuel nozzles. The burner equipment is simplified, since the suction draws the combustion air into the furnace,

and it may also draw in the gas, if gas is used for fuel. In the latter case gas or air compressors may be dispensed with.

The oven heating system to which my invention is applied comprises essentially a furnace, a series of flues, referred to hereafter as aradiator, supply and return conduits connecting the radiator with the combustion chamber of the furnace in a continuous closed circuit, and a gas impeller in the circuit for circulating the heated gases from the furnace, through the radiator and back to the furnace.

To a system of the type just described above is added the improvement constituting my in-.

vention, namely, an exhauster for maintaining a sub-atmospheric pressure throughout the furnace, the combustion chamber, the supply conduits, and the radiator system. The gas that this exhauster discharges from the enclosed circuit is replaced by fresh air to support combustion drawn into the furnace through a restricted duct or opening.

A preferred embodiment of my invention is illustrated in the accompanying drawings, of which:

Fig. 1 is an isometric view, showing diagrammatically a complete operating assembly as employed to heat a single-lap travelling tray oven.

, Fig. 2 is a fragmentary longitudinal section of the fuel burner and the furnacetaken along line 3-3 of Fig. 1.

Referring to Fig. 1, numeral 1 designates the outline of the oven. For purposes of illustration I have shown a heating system installed in a traveling tray oven, but it is equally applicable to an oven of any other type; The furnace 2 is provided with a gas or oil burner 3 of any suitable type. The combustion air is drawn in by suction through an inlet pipe 4. The inlet 4 is so restricted in capacity that even when the minimum volume of gases is being discharged from the circulating system the desired condition of partial vacuum will be maintained in the furnace. This restriction may be accom plished by limiting the size of the inlet, in

which case the quantity of combustion air drawn in will be. adjusted by increasing or decreasing the ,volume of gas vented out of the system. In this case the permanent opening will be small enough to maintain the desired degree of suction when the burner is operating at its lowest rate. It is referable, however, to vent out of the circu ating system the minimum volume of gas necessary to maintain the partial vacuum and to recirculate as much of the gases as possible. To

make this possible the restriction ofinlet 4.

Within the baking chamber of the oven, depending upon its size. The form of these radiators will vary with the design of the individual ovens to which they may be applied, and is' immaterial to the invention. The form which I have illustrated comprises an inlet and an outlet header, 7a and 70 respectively, connected by radiator flues 7b..

9 is preferably located in the cool gas return conduit 8, but may be placed elsewhere in the system, when a separate exhauster independent of fan 9 is used to positively induce a sub-atmospheric pressure Within the system.

The sub-atmospheric pressure within the heating system can be maintained by either of two forms of exhauster; first, by a positively acting exhauster independent of the gas-circulating impeller, and second, by providing a suitable vent from the duct system located in the high-pressure zone just in front of the circulating impeller. Vith either of the above means the supply of fresh air to the furnace is restricted so that throughout the range of heat production a greater volume of air will be vented off than is drawn into the furnace.

A preferred form of the first mentioned positive exhauster will now be described. Referring to Fig. 1, an aperture 11 in conduit 8 opens into an exhaust conduit 17, which communicates with the inlet to an exhaust fan 14, driven by a motor 15. A damper 12 controls the volume of gas drawn through conduit 13. The fan 14 is preferably arranged to exhaust the gas through a stack to the atmosphere.

While it is not essential to the successful maintenance of a sub-atmospheric pressure in the furnace and radiators that the fan be connected to the circuit at any particular exhausting from the duct system located just ahead of the gas impeller. Referring to Fig. 1, the exhaust fan 14 is omitted, and the ex haust pipe 13 is caused to discharge directly to the atmosphere through a suitable stack (not shown). The aperture 11 into pipe 13 from conduit 8 then constitutes the vent, mentioned above, and the gas discharged from the circulating fan 9 will tend to flow out of the system through the vent. I have discovered that a plus pressure may exist in front of the fan 9 simultaneously with a minus pressure in the furnace and the subsequent portions of the system, without the use of any dampers or other special flow-impeding devices. By suitably proportioning the size and length of conduit 8, the size of the vent aperture 11, and the normal flow of fuel and air to the furnace, to the capacity of the fan, the system can be readily made to operate inherently according to the principle of the invention.

To permit of the adjustment of the system to varying heating demands,- adjustable dampers and valves have been provided as follows: A valve or damper 16 in conduit 8 between the exhaust opening 11 and the furnace 2 can be adjusted to produce any desired degree of pressure behind it. By adjusting this damper 16 and the exhaust-pipe valve 12 the proportion between the volume of gas exhausted and the volume of gas recirculated may be altered as desired. If the valve 16 should be closed all the way and valve 12 opened, a maximum of gas will be discharged through the exhaust pipe and none will be recirculated.

Using either of the above-described suction-producing systems, dampers 12 and 16 will be adjusted to vent oflf the amount of gases required to produce the desired minus pressure in the furnace and radiating flues. Their setting will depend upon the Volume of fresh air admitted through inlet 4 and the amount of fuel being admitted to the burner 3, and they will be adjusted so that the volume of gas exhausted from the system is enough greater than the volume of fresh air and fuel gas drawn into the furnace through inlet pipe 4 to reduce the pressure of gases within the furnace 2, the supply conduit 6, and the flue radiator 7 slightly below that of the atmosphere.

A fresh air intake opening 17 controlled by a valve 18, is installed in conduit 8 beyond the damper 16. By closing damper 16, opening damper 12, and running the circulating fan 9 with valve 18 open, fresh air will be drawn into the system and circulated through the furnace 2, the conduits 6, 8 and radiator system 7 This is done before lighting up the furnace to insure that no explosive gases will be present in the system. This ventilating operation may also be used to reduce the oven temperature quickly when desired.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In combination a bake oven having a flue radiator therein, a furnace having a gasair burner, conduits connecting the combustion chamber of the furnace with the radiator in continuous closed circuit, a gas impeller located within said closed circuit and power-driven, an exhaust fan operative independently of said impeller and having'its intake side in communication with said circuit between the outlet of said radiator and the inlet to said furnace, for maintaining pressure less than atmospheric within the radiator and within the furnace chamber, said exhaust fan arranged to discharge outside of said circuit.

2. In combination a bake oven having a w radiator therein, a furnace, conduits connecting said radiator with the combustion chamber of said furnace in continuous closed circuit, a gas impeller located within said closed circuit, an exhauster in communication with said circuit and a restricted fresh air inlet to said furnace of size so proportioned to the capacity of said exhauster that the pressure within said radiator and furnace is maintained at less than that of the atmosphere when said furnace and exhauster are in operation.

3. In combination, a bake oven having a flue radiator therein, a furnace having a fuelair burner, a restricted combustion air inlet to said furnace, conduits connecting the combustion chamber of said furnace with the radiator in continuous closed circuit, a powerdriven gas impeller within said closed circuit to maintain continuous circulation of gases of combustion through the circuit, and a valved gas vent to the atmosphere from said circuit located between the pressure side of said impeller and said furnace, adapted to vent oil a volume of gas larger than the volume of air entering the furnace to maintain a sub-atmospheric pressure in that part of the circuit which includes said furnace and said radiator.

4. In combination, a bake oven having a flue radiator therein, a furnace, a valvecontrolled air inlet to said furnace, conduits connecting said furnace with said radiator in continuous closed circuit, a gas impeller Within said closed circuit to maintain continuous circulation of the gases of combustion through said circuit, and means for discharging gases from said circuit to the atmosphere in such quantity as to maintain a sub-atmospheric pressure in that portion of said circuit including said furnace and said flue radiator.

In testimony whereof, I afiix my signature.

' EUGENE OSCAR ENGELS 

